Opposite words for flaw:
adornment, embellishment, ornament, decoration, enhancement.
Usage samples:
  1. " One of these has got a flaw, and it's cloudy," he mumbled.
    "The Further Adventures of Jimmie Dale", Frank L. Packard.
  2. I know not why the manoeuvres of Miss Flaw especially attracted me that evening, but I leaned out across Miss Marks and I caught Miss Flaw's eye.
    "Father and Son", Edmund Gosse.
  3. There must have been a flaw somewhere.
    "The Mayor of Warwick", Herbert M. Hopkins.
  4. There is not the smallest flaw in the will.
    "The Scarlet Feather", Houghton Townley.